Potent and specific inhibition of the biological activity of the type-II transmembrane serine protease matriptase by the cyclic microprotein MCoTI-II

Matriptase is a type-II transmembrane serine protease involved in epithelial homeostasis in both health and disease, and is implicated in the development and progression of a variety of cancers. Matriptase mediates its biological effects both via as yet undefined substrates and pathways, and also by proteolytic cleavage of a variety of well-defined protein substrates, several of which it shares with the closely-related protease hepsin. Development of targeted therapeutic strategies will require discrimination between these proteases. Here we have investigated cyclic microproteins of the squash Momordica cochinchinensis trypsin-inhibitor family (generated by total chemical synthesis) and found MCoTI-II to be a high-affinity (Ki 9 nM) and highly selective (> 1,000-fold) inhibitor of matriptase. MCoTI-II efficiently inhibited the proteolytic activation of pro-hepatocyte growth factor (HGF) by matriptase but not by hepsin, in both purified and cell-based systems, and inhibited HGF-dependent cell scattering. MCoTI-II also selectively inhibited the invasion of matriptase-expressing prostate cancer cells. Using a model of epithelial cell tight junction assembly, we also found that MCoTI-II could effectively inhibit the re-establishment of tight junctions and epithelial barrier function in MDCK-I cells after disruption, consistent with the role of matriptase in regulating epithelial integrity. Surprisingly, MCoTI-II was unable to inhibit matriptase-dependent proteolytic activation of prostasin, a GPI-anchored serine protease also implicated in epithelial homeostasis. These observations suggest that the unusually high selectivity afforded by MCoTI-II and its biological effectiveness might represent a useful starting point for the development of therapeutic inhibitors, and further highlight the role of matriptase in epithelial maintenance.

Abstract S6-05: High levels of APOBEC3B, a DNA deaminase and an enzymatic source of C-to-T transitions, are a validated marker of poor outcome in estrogen receptor-positive breast cancer

Two recent observations have connected the innate immune DNA cytosine deaminase APOBEC3B to the genetic evolution of breast cancer. First, APOBEC3B was shown to be up-regulated in the majority of breast cancers, and, in breast cancer cell lines, its activity was causally linked to a doubling of the number of C-to-T transitions over time and to a delay in cell cycle progression (1). Second, sequencing of the complete genome of 21 breast cancers independently suggested that APOBEC deaminase activity could be responsible for 2 of 5 mutational imprints identified, which involved clustered (also called kataegis) and dispersed C-to-T transition mutations in the context of 5’TC dinucleotide motifs (2).

In the current study, we addressed a possible association of APOBEC3B expression with outcome in clinical breast cancer. For this we measured using real-time RT-PCR APOBEC3B mRNA levels in 1,491 primary invasive breast cancers and correlated these levels with disease-free survival (DFS), metastasis-free survival (MFS) and overall survival (OS) using univariate and multivariable Cox regression analysis. In addition, we independently validated our findings in available gene expression datasets with appropriate follow-up.

In univariate analyses including all patients, increasing levels of APOBEC3B mRNA analyzed as a continuous variable were significantly associated with shorter DFS, MFS and OS (Hazard Ratio [HR] = 1.29, 1.31 and 1.36, respectively, all P<0.001). To determine the relation of APOBEC3B mRNA expression with the natural course of the disease without the potential confounding effects of systemic adjuvant therapy, we restricted our next analyses to MFS in 829 patients with lymph node-negative disease who had not received any (neo)adjuvant systemic therapy. This analysis showed that APOBEC3B mRNA expression was, in univariate, and in multivariable analysis, including the traditional prognostic factors (age, menopausal status, tumor size, grade and steroid hormone receptors), a marker of pure prognosis specifically in patients with estrogen receptor-positive (ER+) disease (univariate HR = 1.30; P = 0.003; multivariate HR = 1.22, P = 0.042).

To substantiate and validate our findings, we analysed 4 independent available datasets containing in total 5,760 breast cancer cases in which APOBEC3B mRNA expression was measured by probes on microarrays and found that higher APOBEC3B mRNA expression (dichotomised by mean) was significantly associated with poor outcome in all 4 cohorts ([Metabric, 1,491 ER+ cases, HR = 1.82; P<0.001], [Affymetrix compiled dataset-1, 2,407 cases, HR = 2.22; P = 0.001], and [BIG 1-98; 1,207 cases, HR = 2.13; P<0.001 of late recurrence>5 years], and [Affymetrix dataset-2, 643 ER+ cases, HR = 2.04; P = 0.001]).

Altogether, our analyses show that APOBEC3B mRNA - and as a result likely DNA deamination – is a validated predictor of poor outcome in breast cancer, supporting the notion that APOBEC3B is a potentially interesting clinical target for therapeutic intervention to prevent breast cancer progression and metastasis, particularly in ER+ disease.

1. Burns, M.B. et al. Nature 494, 366-70 (2013); 2. Nik-Zainal, S. et al. Cell 149, 979-93 (2012).

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr S6-05.

Abstract PD10-03: Predictive value of a proliferation score (MS) in postmenopausal women with endocrine-responsive breast cancer: results from International Breast Cancer Study Group (IBCSG) Trial IX

Background: While representing the largest fraction of women diagnosed with primary breast cancer, older postmenopausal women with ER+, HER2− tumors are less responsive to chemoendocrine therapy than younger women and have been underrepresented in molecular profiling of randomized trials. IBCSG Trial IX, a randomized controlled trial in postmenopausal women, median age 61y, with node negative disease, failed to demonstrate the benefit of preceding tamoxifen (T) by 3 cycles of CMF for ER+ tumors. We sought to determine if MS, a proliferation score, could identify a subset of women who differentially benefit from addition of chemotherapy to T in this trial.

Methods: From 1988–1999, 1669 eligible patients (1040 with ER+, HER2− tumors) were randomized to CMF→T vs T. Disease-free survival (DFS) was the primary trial endpoint; breast cancer-free interval (BCFI) which excludes second (non-breast) malignancies and censors deaths without prior cancer event was also evaluated. Analysis was limited to the first 7 years of follow-up. From 671 (ER+, HER2−) available subjects, 568 were successfully profiled by RT-PCR. The mRNA expression levels of 14 equally-weighted proliferation genes and 3 normalization genes were used to generate MS; predetermined binary categorization of MS was used. Analysis of this post hoc, pre-specified study used results from centralized laboratory IHC and Cox models to assess the predictive value of MS on DFS and BCFI, adjusting for traditional risk factors of local treatment, age, ER, PR, Ki67, tumor size and grade.

Results: Subgroups of MS (low, 169 samples (30%) and high, 399 samples (70%)) were identified. MS by treatment interaction was significant for DFS and BCFI (each p ≤ 0.004). Among patients with low MS, CMF→T improved DFS (HR 0.19, 95% CI 0.06–0.59) and BCFI (HR 0.19, 95% CI 0.05–0.72) vs T; 7y DFS was 95% vs 83% with CMF→T vs T. Among patients with high MS, CMF→T did not improve DFS (HR 1.27, 95% CI 0.79–2.05) or BCFI (HR 1.37, 95% CI 0.80–2.33) and 7y DFS of 81% for CMF→T and T. Continuous MS was moderately correlated with log Ki67 (r = 0.47) but not correlated with ER or PR. The MS by treatment interaction remained significant with Ki67 in the model.

Conclusions: Low MS was associated with differential benefit favoring those women receiving CMF→T vs T alone for both DFS and BCFI in the first 7 years. The effect was independent of traditional risk factors including Ki67. Hence this study, which is unconfounded by chemotherapy-induced ovarian ablation in younger women, identifies a subset of postmenopausal women with ER+, HER2− tumors that benefit from CMF chemotherapy. This seemingly incongruous observation is consistent with a) the prior observation that only the low-proliferation subgroup by PAM50 11-gene signature benefits from the addition of weekly paclitaxel to adjuvant FEC (GEICAM/9906), b) the ability of MS to identify a subset of women with tumors with disseminated luminal progenitor cells activated through the agonistic activity of tamoxifen, and c) the repetitive dosing of cyclophosphamide and taxol being hypothesized to act via tumor stroma/anti-angiogenesis. The relative contribution of these factors is under investigation.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr PD10-03.

Haemophilus influenzae serotype B (Hib) seroprevalence in England and Wales in 2009

A national seroprevalence study was performed to determine the prevalence of Haemophilus influenzae type b (Hib) antibodies in England and Wales in 2009, when Hib disease incidence was the lowest ever recorded. A total of 2,693 anonymised residual sera from routine diagnostic testing submitted by participating National Health Service hospital laboratories were tested for Hib anti-polyribosyl-ribitol phosphate (PRP) IgG antibodies using a fluorescent bead assay. Median anti-PRP IgG concentrations were highest in toddlers aged 1–4 years (2.65 μg/ml), followed by children aged 5–9 years (1.95 μg/ml). Antibody concentrations were significantly lower after this age, but were still significantly higher among 10–19 year-olds (0.54 μg/ml) compared with adults aged >20 years (0.16 μg/ ml; p<0.0001). Half of the adults (51%) did not have Hib antibody concentrations ≥0.15 μg/ml, the level considered to confer short-term protection. Thus, the current excellent Hib control appears to be the result of high anti-PRP antibody concentrations in children aged up to 10 years, achieved through the various childhood vaccination campaigns offering booster immunisation. The lack of seroprotection in adults emphasises the importance of maintaining control of the disease and, most probably carriage, in children, therefore raising the question as to whether long-term routine boosting of either pre-school children or adolescents may be required.

mRNA profiling of the cancer degradome in oesophago-gastric adenocarcinoma

Background:

Degradation of the extracellular matrix is fundamental to tumour development, invasion and metastasis. Several protease families have been implicated in the development of a broad range of tumour types, including oesophago–gastric (OG) adenocarcinoma. The aim of this study was to analyse the expression levels of all core members of the cancer degradome in OG adenocarcinoma and to investigate the relationship between expression levels and tumour/patient variables associated with poor prognosis.

Methods:

Comprehensive expression profiling of the protease families (matrix metalloproteinases (MMPs), members of the ADAM metalloproteinase-disintegrin family (ADAMs)), their inhibitors (tissue inhibitors of metalloproteinase), and molecules involved in the c-Met signalling pathway, was performed using quantitative real-time reverse transcription polymerase chain reaction in a cohort of matched malignant and benign peri-tumoural OG tissue (n=25 patients). Data were analysed with respect to clinico-pathological variables (tumour stage and grade, age, sex and pre-operative plasma C-reactive protein level).

Results:

Gene expression of MMP1, 3, 7, 9, 10, 11, 12, 16 and 24 was upregulated by factors >4-fold in OG adenocarcinoma samples compared with matched benign tissue (P<0.01). Expression of ADAM8 and ADAM15 correlated significantly with tumour stage (P=0.048 and P=0.044), and ADAM12 expression correlated with tumour grade (P=0.011).

Conclusion:

This study represents the first comprehensive quantitative analysis of the expression of proteases and their inhibitors in human OG adenocarcinoma. These findings implicate elevated ADAM8, 12 and 15 mRNA expression as potential prognostic molecular markers.

A structured course teaching junior doctors invasive medical procedures results in sustained improvements in self-reported confidence

Pressure on working hours has led to a decrease in opportunities for training in invasive medical procedures for junior doctors. The effect of a structured course on immediate and medium-term changes in self-reported confidence was investigated. A one-day model-based practical course was run on two separate occasions teaching central venous line placement, lumbar puncture, Seldinger-technique chest drain insertion and knee joint aspiration. Attendees were asked to indicate their confidence in each procedure on a 10-point Likert scale before, immediately after and three months after the course. Significant improvements in self-reported confidence were seen for all procedures which were sustained at three months. Feedback was universally positive. Practical preclinical training may be a useful adjunct to patient-based training in invasive procedures. The course was particularly popular with foundation year trainees: ideally this training should be available before trainees' first exposure in the clinical setting.

Roles and regulation of membrane-associated serine proteases

Pericellular proteolytic activity affects many aspects of cellular behaviour, via mechanisms involving processing of the extracellular matrix, growth factors and receptors. The serine proteases have exquisitely sensitive regulatory mechanisms in this setting, involving both receptor-bound and transmembrane proteases. Receptor-bound proteases are exemplified by the uPA (urokinase plasminogen activator)/uPAR (uPAR receptor) plasminogen activation system. The mechanisms initiating the activity of this proteolytic system on the cell surface, a critical regulatory point, are poorly understood. We have found that the expression of the TTSP (type II transmembrane serine protease) matriptase is highly regulated in leucocytes, and correlates with the presence of active uPA on their surface. Using siRNA (small interfering RNA), we have demonstrated that matriptase specifically activates uPAR-associated pro-uPA. The uPA/uPAR system has been implicated in the activation of the plasminogen-related growth factor HGF (hepatocyte growth factor). However, we find no evidence for this, but instead that HGF can be activated by both matriptase and the related TTSP hepsin in purified systems. Hepsin is of particular interest, as the proteolytic cleavage sequence of HGF is an 'ideal substrate' for hepsin and membrane-associated hepsin activates HGF with high efficiency. Both of these TTSPs can be activated autocatalytically at the cell surface, an unusual mechanism among the serine proteases. Therefore these TTSPs have the capacity to be true upstream initiators of proteolytic activity with subsequent downstream effects on cell behaviour.

AutoCSA, an algorithm for high throughput DNA sequence variant detection in cancer genomes

The undertaking of large-scale DNA sequencing screens for somatic variants in human cancers requires accurate and rapid processing of traces for variants. Due to their often aneuploid nature and admixed normal tissue, heterozygous variants found in primary cancers are often subtle and difficult to detect. To address these issues, we have developed a mutation detection algorithm, AutoCSA, specifically optimized for the high throughput screening of cancer samples.

Behaviour and emotional problems in toddlers with pervasive developmental disorders and developmental delay: associations with parental mental health and family functioning

BACKGROUND

Behavioural and emotional problems occur at a high rate in children and adolescents with intellectual disability, often from a young age. Some studies have indicated that children and adolescents with autism present with even higher rates. Less is known about the presentation, development and family impact of these difficulties in young children with autism. This study aimed to explore these issues in toddlers with pervasive developmental disorders (PDDs), those with delay without a PDD, and their families.

METHODS

Participants were 123 children aged 20-51 months, referred to a developmental assessment clinic. Parents completed a checklist on child behavioural and emotional problems, and individual questionnaires on family functioning, their own mental health, and stress in relation to parenting their child. The child's language and cognitive skills, adaptive functioning and behaviour were assessed by standardized measures. Measures were repeated 1 year postdiagnosis. Behavioural and emotional problems in young children with a PDD were compared with those in children with developmental delay without a PDD, and their impact on parental outcomes explored over time.

RESULTS

Initial and follow-up measures of child behaviour and emotional problems, parent mental health problems, parent stress and family functioning were significantly correlated, providing some evidence of stability over time. Child emotional and behavioural problems contributed significantly more to mother stress, parent mental health problems, and perceived family dysfunction than child diagnosis (PDD/non-PDD), delay or gender. Compared with mothers, all fathers reported significantly less stress in relation to parenting their child.

CONCLUSION

Results highlighted the importance of addressing emotional and behavioural problems in very young children with autism and/or developmental delay. The need for early support and intervention for mothers, fathers and families in this context was also evidenced. As research has shown that behavioural and emotional problems persist into adolescence and young adulthood, understanding of these issues in very young children and their parents has important implications for intervention and long-term outcomes.

Evaluation of a sampling methodology for rapid assessment of Aedes aegypti infestation levels in Iquitos, Peru

An epidemic of dengue during 2001 in Northwestern Peru reemphasized the need for efficient, accurate, and economical vector surveillance. Between November 1998 and January 1999, we carried out extensive entomological surveys in two neighborhoods of approximately 600 contiguous houses located in the Amazonian city of Iquitos, providing a unique opportunity to evaluate the Aedes aegypti (L.) rapid assessment survey strategy. Based on Pan American Health Organization recommendations, this strategy is used by the Peruvian Ministry of Health (MOH). In our analysis all household locations, including closed and unoccupied houses, were georeferenced and displayed in a geographic information system, which facilitated simulations of MOH surveys based on hypothetical systematic sampling transects. Larval, pupal, and adult mosquito indices were calculated for each simulation (n = 10) and compared with the indices calculated from the complete data set (n = 4). The range of indices calculated from simulations was moderately high, but included actual indices. For example, simulation ranges for house indices (HI, percentage of infested houses from complete survey) were 38-56% (45%), 36-42% (38%), 21-34% (30%), and 13-33% (27%) in four surveys. HI, Breteau index, pupae per hectare, adult index, and adults per hectare were more robust entomological indicators (coefficient of variation [CV]/mean = 0.1-2.9) than the container index, pupae per person, pupae per house, adults per person, and adults per house (CV/mean >20). Our results demonstrate that the MOH's Ae. aegypti risk assessment program provides reasonable estimates of indices based on samples from every house. However, it is critical that future studies investigate the association of these indices with rates of virus transmission to determine whether sampling variability will negatively impact the application of indices in a public health context.

Effect of different 5-HT1A receptor antagonists in combination with paroxetine on expression of the immediate-early gene Arc in rat brain

Selective 5-HT(1A) receptor antagonists enhance the effect of selective serotonin reuptake inhibitors (SSRIs) on presynaptic 5-HT function, and have potential as antidepressant augmentation therapies. The present study tested the effect of different selective 5-HT(1A) receptor antagonists (WAY 100635, NAD-299, p-MPPI and LY 426965) in combination with a SSRI (paroxetine), on postsynaptic 5-HT function measured by increased expression of the immediate early gene, Arc. Paroxetine (5 mg/kg s.c.) combined with WAY 100635 (0.3 mg/kg s.c.) increased Arc mRNA in frontal, parietal and piriform cortices, and caudate putamen. Paroxetine (5 mg/kg s.c.) plus NAD-299 (1 or 5 mg/kg s.c.) had a similar effect. None of these drugs increased Arc mRNA when administered alone. Paroxetine (5 mg/kg s.c.) plus p-MPPI (8.5 mg/kg s.c.) also increased Arc mRNA but p-MPPI itself elevated Arc mRNA in many regions. Whilst LY 426965 (3 or 10 mg/kg s.c.) had no effect alone, when combined with paroxetine (5 mg/kg s.c.), the drug increased Arc mRNA in caudate putamen but not cortical regions.In conclusion, this study demonstrates that four 5-HT(1A) receptor antagonists augment the effect of an SSRI on Arc mRNA expression, which is suggestive of increased postsynaptic 5-HT function. However, the data reveal certain differences in the 5-HT(1A) receptor antagonists not recognised in models of presynaptic 5-HT function.

Quality indicators for antibiotic control programmes

Antimicrobial control measures are commonly perceived to lead to an improvement in quality of prescribing, cost-effectiveness and reduction in resistance. All three outcomes have been subject to scrutiny. As proper use of resources needs to be balanced with provision of high-quality health care, the effectiveness of control measures (antibiotic policies or formularies) must be monitored. Measurement of quality by using specific indicators has been suggested as an effective measure of performance. We describe a model for evaluating core aspects of antimicrobial control programmes, aimed at improving the quality of glycopeptide prescribing by 'appropriate use guidelines'. Prioritizing indicator settings within antimicrobial control programmes is essential if limited resources are to be used most effectively. Indicator development, evaluation and feedback ought to be multi-disciplinary to ensure ownership and long-term benefit.

Pathways to HIV testing and care by black African and white patients in London

OBJECTIVE

To examine factors associated with uptake of HIV clinic services by black African HIV positive people living in London.

DESIGN

Questionnaire survey of patients attending study clinic.

SETTING

HIV outpatient clinic in south London, UK.

SUBJECTS

All HIV positive patients attending the clinic between July 1999 and March 2000.

MAIN OUTCOME MEASURES

Use of health services, delay in seeking HIV test, pre-HIV test concerns, delay in uptake of HIV care, barriers to clinic use, disclosure, sources of support.

RESULTS

392 questionnaires were completed. Respondents were 64% white, 26% black African, and 10% from other ethnic groups. Twenty eight per cent of black Africans suspected they were HIV positive before diagnosis (white patients 45% (p<0.01)). Before testing 11% of black Africans had previously attended a genitourinary medicine clinic, 80% had consulted a GP. Twenty per cent of black Africans expressed concern over entitlement to care and where to get an HIV test. The majority of black Africans (66%) received HIV care within 1 month of their diagnosis. They were significantly (p<0.01) less likely than white patients to disclose their HIV status to family and friends.

CONCLUSION

This study suggests that although black Africans are a high risk group for HIV infection they generally do not suspect their status. While they may delay testing, their uptake of HIV clinic care and use of statutory and voluntary support services after diagnosis is similar to their white counterparts. However, they lack informal support networks. This study highlights the continuing need for health promotion work among London's African communities, to reduce the stigma surrounding HIV/AIDS and to raise awareness of the benefits of testing.

Participation of racial/ethnic groups in clinical trials and race-related labeling: a review of new molecular entities approved 1995-1999

Few recent data are available from formal evaluations of approved new drug applications to address perceptions that racial and ethnic groups are under-represented in clinical trials of new drugs. This study reviews racial and ethnic group participation in clinical trials and race-related labeling for new molecular entities approved during a five-year period by the Food and Drug Administration's (FDA) Center for Drug Evaluation and Research (CDER). This was a retrospective review of FDA medical officers' reviews of clinical trial protocols and product labeling for 185 new molecular entities (NME's) approved by CDER between January 1,1995, and December 31, 1999. Enrollment data were obtained from the reviews and tabulated according to race/ethnicity. The approved product labeling was searched for statements related to product testing in various racial/ethnic groups. All data were compiled and analyzed using Microsoft Access. This study quantifies the participation of racial/ethnic groups in clinical trials by year and therapeutic category. Additionally, the study categorizes labeling based on the types of effects described as related to race/ethnicity. Racial and ethnic groups appear to participate in clinical trials to varying degrees. African Americans participated in trials to the greatest extent; however, their participation steadily declined from 12% in 1995 to 6% in 1999. Among trials known to be conducted only in the U.S., African-American participation is comparable to their representation in the U.S. population. In all cases, participants designated as Hispanic appear to be far below their representation in the population. Some differences in participation for all racial and ethnic groups are seen when comparisons from year-to-year or among drug classes are made. Labeling for 45% (84/185) of the products contained some statement about race, although in only 8% (15/185) were differences related to race described. Fifty percent (50%) of the effects were pharmacokinetic, 39% were efficacy, and 11% were safety. One product label recommended a change in dosage based on racial differences.

Provision of drugs for post-exposure prophylaxis of HIV for medical students on overseas electives

OBJECTIVES

To assess the need for, and the most practical way to provide, HIV post-exposure prophylaxis (PEP) for medical students travelling to areas where this is not readily available.

METHODS

Follow-up questionnaire for all 140 students from Dundee University returning from their medical elective in 2000, 22 of whom took triple therapy for PEP with them on elective.

RESULTS

103/140 students (74%) returned questionnaires. 76/103 (74%) were involved in exposure-prone procedures and 38/103 (37%) reported a significant exposure to potentially infective fluids. Six of this group considered PEP but none reported using it. The greatest perceived risk on elective remained road accidents. 87/103 respondents thought a 24-h helpline for health issues on electives would be useful.

CONCLUSIONS

A high number of students report significant exposure to potentially infected fluids and this needs to be urgently addressed. There was almost unanimous endorsement of the idea of providing PEP and when it is made easily available prior to travel, students are willing to take it to areas where it is not available. In response to the survey, the investigators are looking at how to increase the current limited supply of PEP (Students may have to pay part of the cost) and the best way to provide a helpline, as it is felt that this could have a broad impact on student safety on electives, not just for issues involving PEP.

The farnesyl transferase inhibitor SCH 66336 induces a G(2) --> M or G(1) pause in sensitive human tumor cell lines

SCH 66336 is a potent farnesyl transferase inhibitor (FTI) in clinical development. It efficiently prevents the membrane association of H-ras, but not K- or N-ras. Yet, in soft agar, it reverts the anchorage-independent growth of human tumor cell lines (hTCLs) harboring H-ras, K-ras, and N-ras mutations, implying that blocking farnesylation of proteins besides ras may be responsible for this effect. Experiments show that SCH 66336 altered the cell cycle distribution of sensitive human tumor cells in two distinct ways. Most sensitive hTCLs accumulated in the G(2)-->M phase after the FTI treatment, but those with an activated H-ras accumulated in G(1) phase, suggesting that the biological effects induced by FTIs in cells with an activated H-ras are distinct from other sensitive cells. A careful genotypic comparison of the hTCLs revealed that those cells with wild-type p53 are especially sensitive to the FTIs. In these cells p53 and its downstream target gene p21(Cip1) are induced after treatment with SCH 66336 for 24 h. These data suggest that cell cycle effects, either G(1) or G(2)-->M accumulation, and p53 status are important for mediating the effects of FTIs on tumor cells.